This invention relates generally to a variable tip width adjustment system for a continuous casting machine and more particularly to a variable tip width adjustment system having movable end dams located inside the tip nozzle of a roll caster.
The formation and casting of metals and metal alloys of various kinds have been conducted for many years using commercial scale operations. For example, continuous twin roll casters, such as those shown in U.S. Pat. Nos. 2,790,216 and 4,054,173 are commonly used. The casters disclosed therein include an opposing pair of water cooled, counter-rotated and generally horizontally oriented casting rolls. Molten metal is routed through a feed system into the nip of the two rolls just prior to the closest approach of the rolls. Typically, the feed system includes an upstream head box and a feed tip nozzle. The metal is directed from the head box, through the feed tip nozzle and into the nip of the rolls. As the metal comes into contact with the water cooled casting rolls, heat is rapidly extracted and the metal begins to solidify. The solid metal is then compressed into a sheet as it passes through the gap between the caster rolls.
Conventional casters of this type generally have a fixed, non-movable end dam on each side of the tip nozzle. The purpose of the end dams is to prevent the molten metal from flowing outside of the tip nozzle overall width. Typically, to change the casting widths of a continuous strip caster, the caster must be stopped and a new tip nozzle with an alternate tip width installed. This process results in an extended down time of the caster and can be quite costly to customers who routinely cast multiple widths.
Those who are familiar in the art of continuous strip casting and are well versed on the conventional roll type casters have, in the past, illustrated the capability of changing the tip width while casting without requiring a complete halt of the caster. However, the methods previously used were unpredictable and were not common throughout the industry. Known width adjustment systems include the use of a series of plugs, i.e., removable end dams, inserted in the front section of the tip nozzle nearest to the nip of the caster rolls. A series of plugs is located on either side of the tip nozzle. Each plug is approximately 50 mm wide and includes an angle on the side of the plug that faces the metal that simulates an end dam. To widen the width of the strip, the plugs are removed. With the removal of each plug, the strip width is increased axially in an increment equal to the width of each plug removed. For example, if the casting width was originally 1550 mm wide and two plugs are removed, one from each side, the caster width increases to 1650 mm wide. This process can be repeated until the desired tip width is attained.
A disadvantage of the known width adjustment system is that the desired width cannot be attained with repeatable accuracy. Accordingly, it is desirable to provide a variable tip width adjustment system that can provide incremental precision of xc2x11 mm and can attain repeatable accuracy.
Additionally, it is desirable to provide a variable tip width adjustment system that can mechanically move a sliding end dam axially inside the tip nozzle in both directions, thereby allowing the width of the tip nozzle to be narrowed, as well as widened.
Finally, it is desirable to provide a tip width adjustment system that can be applied to new casters or retrofitted to existing roll casting lines.
A variable tip width adjustment system for use in continuous casting of a molten metal includes a feed tip nozzle downstream from a distribution box, the nozzle including a pair of feed tip nozzle members spaced apart to define a feed tip opening at a downstream edge of the feed tip nozzle members and a pair of end dams located on a drive side and an operator side of the roll casters, the end dams slidably engaged inside the tip nozzle, each dam being axially moveable in two directions inside the tip nozzle. The end dams are preferably actuated using a programmable controller and a stepper motor that is responsive to the signals of the programmable controller. In the alternative, the stepper motors could be actuated using a manual controller. The stepper motor, with a gear box, is preferably connected to the end dam via flex connector and a connecting guide rod directed through a guide tube.
The end dams preferably are composed of a material that is non-wetting to molten metal. In the preferred embodiment, the end dam has a thin layer of ceramic fiber paper glued to both the top and bottom surface of the end dam. The tip nozzle is preferably coated with a liquid boron nitride material or other coating having a high lubricity value allowing the moveable end dam to glide inside the tip nozzle without any grabbing or binding.